This application claims priority to German patent application number 101 42 047.1 filed Aug. 28, 2001.
The invention relates to a wind deflector.
A conventional wind deflector comprises an operating element for a sliding roof system, the wind deflector being movable by means of the operating element between a raised position and a lowered position. Such a wind deflector is known, for example, from DE 198 02 301 A1. In this wind deflector, there is provided a separate wind deflector electric motor which can be driven independently of the electric motor that is used for shifting a sliding roof cover of the sliding roof system.
The disadvantages of this known wind deflector are the high constructional expenditure and the high costs, in particular for the separate electric motor.
It is the object of the invention to further develop a wind deflector of the type initially mentioned to the effect that at a low constructional expenditure it can be moved between the lowered position and the raised position independently of the actuation of the sliding roof cover.
According to the invention, a wind deflector includes an operating element for a sliding roof system. The wind deflector is movable by means of the operating element between a raised position and a lowered position. The operating element consists of a shape memory alloy so that as a function of its temperature it can assume one of a first and second states. Such a shape memory alloy is also known as xe2x80x9ctwo-way memory alloyxe2x80x9d. In the initial state, the alloy has a martensitic state. If the alloy is heated up beyond the martensitic transformation temperature, its crystal lattice arrives at the austenitic state. It is in this state that the operating element undergoes a change in shape through which the operating element is able to perform work. If the shape memory alloy cools down again, it returns to the martensitic state. In the process, the operating element returns to its first shape. Such transition between a first and a second state or a first and a second shape can be provoked virtually as often as desired.
For the purpose of changing the temperature of the operating element, there may be provided a power supply which is able to deliver a current flowing through the operating element. In this way the operating element is directly heated by the intrinsic resistance heat dissipation of the shape memory alloy, making possible very short switching times.
A particularly suitable material for the shape memory alloy is a NiTi alloy. This material allows a very high number of cycles. In addition, the transition temperature from the martensitic to the austenitic phase can be set over a wide range.
According to the preferred embodiment of the invention it is provided for that the wind deflector is able to perform an idle stroke without the operating element being shifted. Such an idle stroke is required, for instance, if the wind deflector is shifted by the sliding roof cover when the latter is opened or closed, without the operating element being actuated to this end.
According to the preferred embodiment of the invention it is provided for that the operating element is a wire which in its first state has a first length and which in its second state has a second length. This leads to a particularly compact embodiment. The wire may extend in parallelism to the wind deflector and underneath it. Thus, no additional space is required. During the transition from the martensitic state to the austenitic state, the wire shortens; in so doing, it can exert a comparably high tensile force. In this way high actuation forces can be provided.
A raising spring is preferably provided which biases the wind deflector into the raised position, the wire being able to pull the wind deflector from the raised position into the lowered position. This is particularly of advantage if an electronic control is additionally provided which controls the temperature of the operating element as a function of the wind noise generated by the sliding roof system. As soon as the electronic control detects such wind noise, for instance a thrumming which is a booming noise with very low frequency, the wire may be supplied with current, so that it brings the wind deflector into the lowered position. The resultant change in flow conditions in the sliding roof system is sufficient in many cases to eliminate the thrumming. It may be alternatively provided to retract the wind deflector as a function of the speed if it is known at which vehicle speed the low-frequency booming will occur.
It is preferably provided for that the wire directly engages the wind deflector, the wire extending along a supporting rail for the wind deflector and running through a deflecting element. This embodiment is distinguished by a particularly low constructional expenditure.
According to an alternative embodiment it is provided for that the wire engages a movable intermediate element and that a connecting element is mounted to the intermediate element, the connecting element being connected with the wind deflector. In this arrangement, the intermediate element is preferably a pivoting lever, the wire engaging the pivoting lever at a first radius that is shorter than a second radius where the connecting element engages. This embodiment results in a conversion of the operating stroke of the wire. Thus, the wire may be configured with a comparably short length. The operating forces that are made available by the wire when it shortens, are sufficient in any case to bring the wind deflector from the raised position into an at least partially lowered position, despite the stroke being transmitted.
According to an alternative embodiment, the pivoting lever may also be realized with a horizontally arranged swiveling axis, so that its pivoting arm moves in vertical direction. The pivoting arm may engage the wind deflector directly or by means of an intermediate lever.
Advantageous embodiments will be apparent from the subclaims.